There is often a requirement that a fire rated wall/door systems include a transparent window for aesthetic and security reasons. For example, it is desirable to have important documents retained in vaults which are enclosed by a fire rated wall/door system and to provide for windows in the walls so that the vaults can be easily observed. Also it is desirable to have such secure areas feel as open as possible so that people working therein will have a pleasant environment. Heretofore, fire rated wall/door systems have been limited to having windows in doors which are limited in total area to less than 100 square inches so that the windows can withstand a specified temperature for a specified length of time to receive a required rating. The glass has been limited to glass which is reinforced with a wire mesh. Certainly it would be more desirable to have a larger window that looked like a standard window or door for all of the above indicated reasons and still have the system be able to obtain the required fire rating.
It is to be understood that the need for fire rated wall systems extends from internal wall systems with and without doors to external storefront wall systems with and without doors.
A new transparent glass assembly has recently become available. This system is comprised of first and second panes of toughened or tempered safety glass for 60-minute rating and a third pane for 90-minute rating which are held apart by a metal spacer running about the periphery thereof. The cavity formed between the two panes of glass are then filled with a transparent gel capable of absorbing heat radiation. Heat absorption leads to modification of organic compounds in the gel, forming a dense and highly heat insulating crust after the first pane adjacent the heat is shattered by the heat. This crust slowly propagates itself from the shattered first pane toward the second pane which is not exposed to the heat. During this process the gel does not separate from the second pane. It should be understood that this material not only stops smoke and flames as with prior window material comprised of wired glass or glass brick, but also prevents heat radiation from passing therethrough. Such heat radiation can inflame curtains, furniture, and other flammable materials, even though the flames are contained behind the fire rated wall.
This glass assembly gives rise to the possibility of much larger transparent windows or openings in a fire rated wall/door system. However, the size of such panels gives rise to thermal expansion problems which were not considered previously. Also it should be understood that the periphery of this transparent panel needs to be protected. In the past, such protection has been afforded through the use of wallboard and some fire-resistant materials.
The present invention is provided to overcome one or more of the disadvantages of the prior devices.